In traditional filtration equipment, fluid to be filtered is recirculated through a filter element containing filtration membranes where the fluid is driven parallel to the membrane to permit the membrane to purify fluid as it passes through the membrane, and to provide a scrubbing action on the surface of the membrane to remove built-up solids that have been filtered out of the fluid by the membrane. These filter elements typically have one inlet where the raw fluid is introduced, and two outlets, one where the raw recirculating fluid exits and another where the purified fluid exits.
Many different configurations of ultrafiltration filter elements have been developed which provide this crossflow cleaning action. One type of filter element, called a "spiral" type of filter element, is made of flat sheets of filter material that are made into pouches that are wound into a spiral shape around a porous or perforated center tube. The feed fluid to be filtered enters one end of the filter element and flows parallel to the cylindrical axis of the filter to exit at the other end of the filter as a concentrate stream. The filtered or permeate fluid collects in the pouches and passes in a spiral manner to the center tube for collection. This type of "spiral" design is used currently by many companies to construct both ultrafiltration as well as reverse osmosis filter elements.
Major problems with this type of filter element are that they are expensive to manufacture and cannot be easily mounted on or dismounted from a piece of filtration equipment. In the typical well-known state-of-the-art manufacturing process, individual flat sheets are positioned on a table top, urethane or epoxy adhesive is applied around the perimeters of the alternate sheets, and they are then manually rolled around a center tube to create spiral-shaped pouches hydraulically connected to the center tube. Upon drying of the adhesive, the ends of the rolled filter element are trimmed to remove excess adhesive and open the spaces between the individual pouches to allow the fluid to be filtered to enter the ends of the filter element. Not only is this a slow manual manufacturing process, but also often, when trimming the excess adhesive from the ends of the filters, the pouches can be accidentally ruptured, rendering the filter element useless. Therefore, usually extensive leak testing must be performed on the filter elements before they are released to the customer.
In current, commercial practice, these filters are mounted on a filtration system by being inserted into a filter housing, which is then screwed onto a hydraulic fitting on the filtration system. Fluid to be filtered enters the top of the filter element and flows axially through the filter element to exit at the bottom of the filter. Fluid that has been filtered enters the spirally wound pouches and flows spirally to the center tube for collection.
When the filter element needs changing, the housing must be dismounted from the filtration system and the filter element manually removed from the housing. This results in considerable spillage and operator exposure to the fluid being filtered, where this fluid may be hazardous to the operator and equipment.
It is desirable therefore to provide a spiral wound filter apparatus and method of manufacturing the filter apparatus, which filter apparatus is easily and inexpensively manufactured and wherein the spiral wound filter cartridge used in the filter apparatus can be easily mounted and dismounted on conventional filter apparatuses by an unskilled operator and with minimum contact with any potentially hazardous fluids being filtered. It is desired to provide a method of filtration particularly for the filtration of hazardous solvent or water waste solutions like ink printing blanket waste solution comprising ink and other particles, petroleum solvent and water.